1. Field of the Invention
The present invention relates to a filtration arrangement in a fluid feed system comprising a fluid reservoir, a supply pump, and user circuits supplied with fluid from said reservoir by said pump, and is particularly concerned with such a filtration arrangement for a lubrication circuit of a turbo-engine.
2. Summary of the Prior Art
Supplying a turbo-engine lubrication circuit with lubricating fluid is generally effected in the manner illustrated diagrammatically in FIG. 1 of the accompanying drawings. The lubricating fluid is drawn from a reservoir 1 by a pump 2, usually of the positive displacement type, and passes through a filter 3 before being distributed to the user circuits 4 of the turboengine. A circuit 5 for recovery and return of the fluid from the user circuits 4 to the reservoir 1 completes the installation.
Any interruption in the supply of lubricating fluid to the user circuits in such a system could have catastrophic consequences, especially in aeronautical applications. Consequently, a safety circuit, comprising a by-pass valve 6, is usually mounted in parallel with the filter 3. Thus, when the pressure drop across the filter 3, resulting from clogging caused by the collection of pollutant material from the lubricating fluid passing through the filter 3, exceeds a pre-set threshold, the by-pass valve 6 opens under the action of pressure so that the user circuits 4 continue to be supplied. With such a system, a choice has to be made between two possible alternatives.
In one case the filter arrangement may be completed by means of a relief filter 7 mounted in series with the by-pass valve 6 as shown in FIG. 1a, which means that the relief filter 7 is also subject to clogging whenever the main filter of the fluid supply circuit is by-passed. This arrangement also has other drawbacks, particularly in an aircraft engine, where the room available is extremely limited for incorporating the equipment and the need for accessibility to the two filters 3 and 7 can make the system a very costly arrangement. In addition, maintenance work takes longer and is more complicated because of the need to replace or clean the two filters 3 and 7, and failure to clean the filters leads back to the original risk of catastrophic interruption of lubrication.
Alternatively, in order to avoid these drawbacks, and particularly for essential reasons of safety, one may choose not to include a relief filter 7 in the by-pass supply circuit incorporating the by-pass valve 6. In this case, however, the user circuits 4 are supplied by a polluted lubricating fluid, which also has obvious drawbacks.